The present invention relates in general to mine roof supports and more particularly to such supports having a main roof-engaging structure linked to an auxiliary roof-engaging structure at its front end.
It is well known to provide an auxiliary roof-engaging structure or extension cap on the main roof cap of a mine roof support which can take the form of a trestle, a shield support and/or a walking support. Such auxiliary roof-engaging structures are used to underpin the roof at the critical forward zone where it adjoins the mineral face. These structure can be designed to slide in and out towards the workface or to swing up and down. It is also known to provide a roof support with a multi-part auxiliary roof-engaging structure which itself is designed for swinging and has a sliding forward extension within or below a rear component pivotably linked to the main cap. This type of sliding extension does not generally underpin the roof over a sufficiently large area since it tends to engage on the roof at discrete separated points. To avoid this problem the sliding extension can be arranged on the rear component so that when the auxiliary structure is braced against the roof under relatively high setting pressure, the sliding extension likewise is braced against the roof over its full area. However in the braced or set condition it is not possible to move the sliding extension in and out and it has been necessary for personnel to manually adjust the setting pressure to permit adjustment of the sliding extension. This largely emperical control is disadvantageous since it can lead to temporary removal of all support for the roof over the critical forward zone which can result in partial roof collapse. A general object of the present invention is to provide an improved roof support structure.